This invention relates to coal firing systems, and, more specifically, to a burner of relatively small capacity that is particularly suited for use in small air heater or furnace applications.
Coal fired systems per se are not new. That is to say, the prior art is replete with examples of various types of coal-fired systems that have heretofore been available in the prior art for purposes of fulfilling the requirements of a multiplicity of diverse applications. However, irrespective of the particular form which the coal-fired system may take or the particular application in which it is being utilized, there is one major operating component which all such coal-fired systems embody; namely, a burner.
Basically speaking, the function of any type of burner, regardless of whether the burner is designed for burning coal or some other type of fuel, is to supply air and fuel to a combustion chamber in the amounts required to support the combustion of the fuel in the chamber. More specifically, desirably the burner should be operative to supply air and fuel to the combustion chamber in such a manner as to produce the following: stability of ignition; effective adjustment for control of ignition point and flame shape; completeness of combustion; uniform distribution of excess air and temperature leaving the combustion chamber; freedom from localized slag deposits; protection against overheating, internal fires and excessive wear in the burner; and accessibility for adjustment and maintenance.
Coal has long been one of this nation's most abundant sources of fuel. At one time earlier in this century, much of the nation's energy needs were being met through the use of coal. Then, a decline set in in the degree to which coal was being employed to generate power. Much of this decline stemmed from the increased usage of oil and gas as sources of fuel. More recently, the power being generated from the burning of oil and gas has been supplemented by the use of nuclear fuel for power producing purposes. However, with the advent of the oil embargo earlier in this decade, which was accompanied by sharp increases in the price of oil and the existence of restricted oil supplies, and the increased concern, which has since been expressed over the rate at which the world's known oil reserves are being depleted, coal has begun to regain much of the favor, which it once had, as a source of fuel to meet the nation's energy needs. To an increasing extent, this has been evidenced in the number of orders which have been placed in recent years, for power generating systems that are to be coal-fired systems as well as the extent to which increased interest is being shown in effecting the conversion of existing oil- and gas- fired power generating systems to coal-fired systems.
By and large, however, the shift, which has been taking place, from oil and/or gas back to coal has been limited to relatively large applications. For purposes of this discussion, a large application is considered to be any application wherein there is a need to provide a heat input, which is in excess of fifty million BTU/Hr. Furthermore, insofar as concerns the coal-fired applications to which reference is had herein, it should be noted that the form of coal, which is actually being burned therein, is pulverized coal. Finally, note is taken of the fact that the coal-fired systems that are presently being marketed embody many significant advances as compared to coal-fired systems of earlier vintage. For the most part though, the focus insofar as concerns the state of the art of coal-fired systems has been on increasing the heat input obtainable from a given coal-fired system and/or rendering the coal-fired system as non-pollutant as required to achieve air pollution standards, etc. In summary, the advances, therefore, which have been alluded to above, now render it possible to offer in the marketplace coal-fired systems of increasingly larger rating as compared to the coal-fired systems that have previously been available.
As noted previously hereinabove, two important factors to which consideration must be given in providing burners of any type, including those intended for utilization in coal-fired systems as one of the major operating components thereof, are flame length and flame stability. It is well recognized by those skilled in the art that the length of the flame produced in the course of the operation of a coal burner wherein pulverized coal is being burned is measurably longer than the length of the flame produced by an oil or gas burner of the same relative rating. The longer flame length in the case of the coal burner is attributable principally to the need to effect the proper mixture of air and fuel required to support combustion. Namely, the mixture of primary air and pulverized coal, which is fed to the coal burner, must be supplemented with secondary air to provide the proper ratio for the combustion of the air and the fuel. More specifically, there is a need to effect the infusion of the oxygen from the air through the carbon particles contained in the pulverized coal in order that combustion may occur. The result, consequently, is a relatively long flame as compared to the flame produced from either oil or gas.
As regards the matter of flame stability, the latter is dependent upon the amount of heat, which is readily available from the fuel that is already burning in the combustion chamber. Generally speaking, flame stabilization is commonly achieved by virtue of a strong vortex, which is created in the combustion chamber and which is operative to divert hot gases of combustion back toward the incoming fuel stream being discharged from the burner.
From the foregoing, it should be readily apparent that a definite relationship exists between combustion chamber size, i.e., furnace area, and the capacity to develop a flame of suitable length and stability. Heretofore, for the most part, furnace area has not been a limiting factor in the employment of prior art forms of coal burners as relates to their ability to achieve therewith, desired flame length and flame stability. This is because the furnace area, i.e., combustion chamber size, has been of sufficiently large dimensions as to not impose any limitations on generating a flame of the desired length. Likewise, there has existed sufficient area therewithin for the development of the strong vortex needed to effect flame stabilization. Moreover, insofar as concerns the conversion of existing facilities to coal or the building of new facilities designed to employ coal-fired systems, the trend has been towards larger capacity units wherein size limitations are not a factor with regard to the attainment of suitable flame length and/or flame stability. This trend towards the utilization of coal rather than oil or gas in connection with such larger capacity units is quite natural. Namely, in the face of a need to conserve scarce natural resources, it is not to be unexpected that attention would be turned first to applications that involve the consumption of larger quantities of fuel and, accordingly, applications in which there exists the potential of achieving the largest savings of fuel.
Recently, however, increasing attention has been directed towards the effectuation of the conversion from oil or gas to coal of even those thermal processes that require heat inputs of relatively small magnitude, i.e., heat inputs of between one million and fifty million BTU/Hr. Much of this is attributable, at least in part, to the continuing rise in the price of oil and gas, and, in part, to a better appreciation by users of oil and gas of their vulnerability to the imposition of restrictions on their usage of oil or gas. Moreover, as a consequence of this increased interest, a need has been established for a new form of coal-fired system that would be suitable for use in those applications wherein heat inputs of between one million and fifty million BTU/Hr. are required. More specifically, the interest in converting more and more of the thermal processes that involve the utilization of relatively small amounts of heat input from oil and gas to coal has generated a need for a coal burner suitable for use in small air heater or furnace applications; namely, a need for a coal burner that is capable under such circumstances of providing a flame of relatively short length accompanied by the desired degree of flame stability. The reason for the need for such a coal burner stems from the fact that the relatively confined nature of the combustion chamber that such small air heaters or furnaces embody renders existing coal burners generally unsuitable for use therein. That is, it is difficult with known forms of coal burners to attain the short flame length and flame stability that desirably should be present during combustion. This is because of the constraints due to size that are imposed by virtue of the fact that the combustion chambers in the aforereferenced small air heaters and furnaces are of relatively small dimensions.
It is, therefore, an object of the present invention to provide a new and improved burner suitable for use in burning, particularly pulverized coal.
It is an another object of the present invention to provide such a burner of relatively small BTU rating.
It is still another object of the present invention to provide such a burner, which is particularly suited for use in small air heater and furnace installations requiring heat inputs of between one million and fifty million BTU/Hr.
A further object of the present invention is to provide such a burner, which embodies a multiplicity of jets, each defining an individual path of flow for fuel through the burner.
A still further object of the present ivnention is to provide such a burner, a characteristic of which is the relatively short flame length that is produced thereby.
Yet another object of the present invention is to provide such a burner with which it is possible to attain short flame length as well as flame stabilization.
Yet still another object of the present invention is to provide such a burner, which is capable of being employed as original equipment in the case of new installations equipped with coal-fired systems, as well as being capable of employing as a replacement burner in the case of existing installations that are being converted from oil- or gas- fired systems to coal-fired systems.
Yet still a further object of the present invention is to provide such a burner, which is advantageously characterized by the fact that because of low turbulence or vortex, it has a low pressure drop, and therefore requires only low primary and secondary air fan horsepower.